The present invention relates to a single handpiece for dental instruments that can be used for ultrasonic scaling when used with an ultrasonic scaling insert, and can be used to abrasively clean teeth when used with an air-abrasive insert. A unique switching system makes possible the use of a number of different kinds of inserts in the same handpiece. A method and apparatus for precise control of magnetostrictive and/or electrostrictive transducers is also provided. The method and apparatus for control of the transducer is discussed with reference to a dental prophylaxis unit; however, it is applicable to any application which requires the precise control of electrical, mechanical or electro-mechanical systems.
1. PRIOR ART
Warrin et al, in U.S. Pat. No. 4,492,574 teach an ultrasonic endodontic dental handpiece having a coil for establishing an alternating magnetic field, the housing having a cooling fluid inlet at one end and being open at the other end for receiving and supporting a removable insert.
Rzewinski, in U.S. Pat. No. 4,494,932 teaches an apparatus for dispensing cleaning powder in an air stream to be directed onto the surface of teeth. The apparatus includes a fluid tight chamber for containing a supply of cleaning powder. Air under pressure is directed into the chamber, and an outlet in the sidewall of the chamber permits air and powder to flow out under pressure.
2. BACKGROUND
Stains on teeth may originate from various sources or causes including smoking, tobacco chewing, excessive drinking of tea or from vegetable origin. Calculus is of several different types, especially serumal and salivary, and calculus deposits ordinarily accumulate in pockets between the teeth and the surrounding soft tissues, the serumal calculus originating from the saliva. These constituents precipitate and bond themselves to the exposed tooth surfaces.
Various techniques and equipment are already known and used in the cleaning of teeth, including hand instruments, rotary rubber cups carrying an abrasive paste of pumice for example, all of which techniques may be used effectively in the removal of calculus, but none of which techniques are satisfactory in effecting the removal of various types of stain, especially the removal of stain from broad areas of the teeth.
It is known in the art to clean teeth using ultrasonic scaler inserts. In an ultrasonic scaler, vibrational motion of a transducer is transformed to flexural or elliptical motion of an insert tip. This motion of the tip is used to dislodge calculus from the teeth. The scaler also has means for irrigating the area where the scaler tip is used by dispensing a liquid, most frequently water, through or over the surface of the scaler tip.
It is also known in the art to clean teeth using air-abrasive equipment which is particularly useful for removing stains from crevices in the teeth.
In the use of air-abrasive equipment for dental purposes, the delivery and dispersal of abrasive particles in air suspension in the mouth is objectionable and in some prior equipment employed for tooth cutting, vacuum means has been employed to capture the abrasive particles. This, however, is bulky and cumbersome. In some prior systems it has also been contemplated to wash the teeth with water following the abrasive treatment, but such subsequent washing does not overcome the objectionable initial distribution of the abrasive particles on the soft tissues and other parts of the mouth. To overcome these difficulties and to provide air-abrasive prophylaxis equipment adapted to the convenient and effective removal of stain and or calculus in a manner which is simple and which produces minimum discomfort to the patient, a handpiece was provided having a nozzle with an air-abrasive discharge passage, and a water discharge passage surrounding the air-abrasive passage, together with control means by which warmed water was delivered for discharge through the water passage, and the air-abrasive and water streams were coordinated to capture the abrasive particles after they were dispensed.
In the handpiece provided in the prior art, the water discharge passage is directed to impinge upon the surface of the tooth being cleaned in an area immediately adjacent to or overlapping the area of impingement of the air-abrasive stream. Preferably a water stream is provided to form a curtain surrounding the air-abrasive stream. In its most effective embodiment, the motion of the powder and liquid as it is being dispensed from the handpiece causes a mixing of the powder and water to form a slurry. It is a slurry of polishing powder and water which provides the most effective cleaning of teeth.
The practitioner has found it most convenient and effective to use both the ultrasonic scaler and the air-abrasive systems described above to provide prophylactic treatment of the teeth. Using both systems, however, requires two sets of equipment, or at least two handpieces: a handpiece for ultrasonic scaling for calculus and plaque removal, and a second handpiece for air-polishing stain and plaque removal. In addition, a water heater is desirable for use with the air-abrasive portion of the device. Since space is usually at a premium in the operatory, the disadvantages of using the described equipment is apparent. In addition, it is bothersome and time consuming for the practitioner to change handpieces in the middle of a treatment.
The prior art systems for driving the scaler insert of the handpiece comprise a magnetostrictive transducer, a signal generator, a power supply and some form of feedback.
The known feedback systems can be divided into three classes. In the simplest form of feedback, the voltage is a function of frequency and is related to the sum of all internal phase shifts. This form of feedback is practical for use only in high quality transducers designed to operate at a specific frequency range in which the induced voltage values are small.
Systems which rely on purely electrical feedback comprise a second feedback system. These two systems have the following shortcomings:
1. The system may start up in either of two different phase conditions, resulting in very different mechanical outputs. PA1 2. In one of the possible phase conditions, impedence in the system may cause reactance in the no-load condition resulting in reduced start-up capability. PA1 3. If the system must be capable of handling high loads, it usually operates with reduced efficiency at lower loads. PA1 4. The tuning of the system must always be a compromise between higher efficiency and start up requirements. PA1 1. Precise control of system operation at the maximum mechanical output point. PA1 2. Improved starting both under load and at no-load conditions. PA1 3. Increased acoustic load capability. PA1 4. Allows for manipulation of system parameters. PA1 5. Increased electro-mechanical operating efficiency. PA1 6. System operation point not affected by power supply variations. PA1 7. No tuning control is required. PA1 8. Allows for expanded operating frequency range.
The third system utilizes a velocity feedback measurement. In this system the vibration pick up voltage controls a generator whose gain is a function of the voltage across the load and the velocity difference between the two ends of the mechanical resonator.
In this system the velocity feedback is either resonated or otherwise wave shaped to provide unambiguous frequency information to the amplifier. It is said in the prior art that this is a requirement to utilize the velocity pick up signal.
It is the object of the present invention to overcome the above described difficulties with the prior art.